Process for electrocoating

Abstract

A coating composition for electrodeposition contains water soluble or water dispersible resin and at least one water soluble oxy-acid salt being selected from the group consisting of stannates, molybdates, tungstates, vanadates and borates, or a mixture of said water soluble oxy-acid salts. The coating formed from said composition on a metallic surface by electrodeposition is excellent in the adhesiveness and anti-corrosive property.

What is claimed is: 
     
       1. A method for preparing electrodeposition coating on an uncoated metallic article which is characterized in that the article desired to be coated is first immersed into an aqueous bath consisting essentially of 4- 10 weight percent of water soluble or water dispersible resin and 0.1 to 0.8% by weight (on the basis of resin solids content) of at least one water soluble oxyacid salt selected from the group consisting of stannates, molybdates, tungstates, vanadates and borates, said article is connected to the positive electrode and supplied with DC electric voltage in the range of 30 to 300 Volts for 30 seconds to 10 minutes, then said article is rinsed with water and dried, and heated at a temperature in the range of 130 to 300° C. for 30 seconds to 60 minutes to cure the resinous component in the obtained electrodeposition coating. 
     
     
       2. A method for preparing electrodeposition coating on an uncoated metallic article as claimed in claim 1, in which said water soluble or water dispersible resin is selected from the group consisting of epoxy resin, melamine-formaldehyde resin, alkyd resin, polyester, acrylic resin, polybutadiene, natural resin and fatty oil derivative. 
     
     
       3. A method for preparing electrodeposition coating on an uncoated metallic article as claimed in claim 1, in which said water soluble oxyacid salt is selected from the group consisting of lithium stannate, sodium stannate, potassium stannate, lithium molybdate, sodium molybdate, potassium polybdate, ammonium heptamolybdate, sodium phosphomolybdate, ammonium phosphomolybdate, lithium tungstate, sodium tungstate, potassium tungstate, sodium metatungstate, sodium paratungstate, ammonium pentatungstate, ammonium heptatungstate, sodium phosphotungstate, barium borotungstate lithium orthovanadate, sodium orthovanadate, lithium metavanadate, sodium metavanadate, potassium metavanadate, ammonium metavanadate, sodium pyrovanadate, lithium metaborate, lithium tetraborate, sodium metaborate, sodiium tetraborate, sodium decaborate, sodium perborate, sodium borate-hydrogen peroxide adduct, sodium boroformate, potassium metaborate, potassium tetraborate, ammonium tetraborate and ammonium biborate. 
     
     
       4. A metallic object electrocoated by the method of claim 1. 
     
     
       5. A method for preparing electrodeposition coating on an uncoated metallic article as claimed in claim 1, in which the amount of said oxy-acid salt is 0.3 to 0.8% by weight on the basis of resin solids content. 
     
     
       6. A method for preparing electrodeposition coating on an uncoated metallic article as claimed in claim 1, in which the steps of immersing the uncoated article into the aqueous bath and the application of electric voltage is effected at a temperature of 20° to 40° C. 
     
     
       7. A method for preparing electrodeposition coating on an uncoated metallic article as claimed in claim 6, in which the amount of said water soluble or water dispersible resin is in the range of 4 to 10% by weight. 
     
     
       8. A method for preparing electrodeposition coating on an uncoated metallic article as claimed in claim 7, in which the amount of said oxy-acid salt is 0.3 to 0.8% by weight on the basis of resin solids content.